As the use of OA equipment has proliferated, it has become necessary to provide measures to counter static electricity within the general office space, and, in particular, in the computer room. Part of such activities concerns the provision of a proper degree of conductivity to the floors.
This type of electroconductive floor can be formed by laying electroconductive flooring sheets, but conventional flooring sheets use carbon black in some form or other as the material which provides conductivity. This creates the problem that the color of the floor must be some shade of black.
In recent years, however, electroconductive flooring sheets which use materials other than carbon black, such as carbon fiber, to provide electroconductivity, have been developed, so that flooring sheets in various colors have made an appearance. It has therefore become possible to install very colorful conductive floors.
However, because electricity will not flow between the installed flooring sheets these sheets must be made conductive in the direction of the thickness, reaching as far as the undersurface, and the sheets must be affixed using an electroconductive adhesive, or metallic joint sheets must be spread out in network form under the flooring sheets. Grounding terminals are generally provided at one or two points for every 100 to 400 m.sup.2 of floor area to ground the floor. In such a case the distance between the locations where the static electricity is produced and the grounding terminal must be about 30 m or less. It is, however, very troublesome to form a network of aluminum foil or thin copper sheeting under the flooring sheets and the quality of work is generally poor. Problems such as exfoliation or bulging occur from loss of adhesive strength.
It is difficult to manufacture an electroconductive adhesive with a low resistance in a method of glueing flooring sheets with an electroconductive adhesive, and a good grounding effect is not necessarily demonstrated in the floor foundation to which the adhesive has been applied. A grounding device must therefore be utilized. In addition, when the grounding terminals are a considerable distance away, the resistance of the path becomes high so that the desired effect is not obtained. A building column is usually used as the grounding terminal, so in a large building such as a factory in which there are few columns there are many cases where it is not practical to provide a grounding terminal in the center of a room. The distance from the point where the static electricity is generated to the grounding terminal is therefore sometimes long. There are also occasions where the adhesive strength of the electroconductive adhesive is not adequate.
Japanese Utility Model Publication 1-29071 discloses a method of forming a joint between electroconductive flooring sheets, using a welding rod 61 with a triangular cross section as shown in FIG. 9, which is made of an electroconductive synthetic resin layer 63 extending from the vertex toward the base of the triangular cross section for almost half the height, with the remaining part of the welding rod 61 being formed from a non-electroconductive synthetic resin layer 65 of the same color as the surface layer of the flooring sheets. The flooring sheets are therefore electrically interconnected.
However, the operation of this type of welding rod is troublesome, and the strength of the formed joint is not always satisfactory.
There are many cases in which there are difficulties in forming an electrically integrated electroconductive flooring sheet when the welding rod 61 is used to form the joints. As illustrated in FIG. 10, when the joint is formed, the end sections of electroconductive long flooring sheets 21, 21 (hereinafter referred to as the flooring sheets 21) are butted together on the floor base 43 and are attached to the floor base by an adhesive 35. The joint grooves are cut out between the adjacent flooring sheets 21, 21 and these grooves are filled with the joint welding rod 61. The joint is then completed by cutting away the portion of the joint welding rod 61 which protrudes from the surface of the flooring sheets 21, 21. In order to make the joint inconspicuous, the surface of the joint should be formed from a non-electroconductive synthetic resin layer 65 which is the same color as a surface layer 21a of the flooring sheets 21. In addition, the flooring sheets 21, 21 are electrically integrated by the underlying electroconductive synthetic resin 63. However, in practice, there are many cases in which the electrical integration of the flooring sheets 21, 21 is inadequate. The reasons for this are as follows.
The flooring sheet 21 is usually formed by laminating a comparatively thin surface layer 21a, which has a low electrical resistance, to a comparatively thick base layer 21b with a high electrical resistance. Then, it is necessary to electrically integrate the surface layers 21a, 21a of adjacent flooring sheets to prevent the electrification of the floor surface. The integration of the adjacent surface layers 21a is provided by the joint welding rod shown in FIG. 10, and because the surface of the joint is formed from the non-electroconductive synthetic resin layer 65, the boundary line between the electroconductive synthetic resin 63 of the joint welding rod 61 and the non-electroconductive synthetic resin layer 65 must be reliably positioned at the thick region of the surface layer 21a. However, in general, the surface layer 21a of the flooring sheet 21 is about 0.2 to 1.5 mm thick, and the total thickness, including the thick base layer 21b, is about 2 to 6 mm. It is difficult to position the boundary line of the joint welding rod 61 in the thick region of the surface layer 21a. In particular this positioning is extremely difficult in consideration of the wide variation in the irregularities in the floor base 43 and the depth of cut of the joint groove.
In addition, it is also known that an electric charge in the floor can be prevented by forming an electroconductive joint using a non-electroconductive flooring sheet or securing with a metal rod (Japanese Laid-Open Utility Model Application 52-141829 and Japanese Laid-Open Patent Application 62-271399). However, with a method of this type, there is a limit to how well the electrification of the floor surface can be prevented so a satisfactory effect is not always obtained.